1. Field of the Invention
The present invention relates generally to semiconductor wafer processing apparatus and, more specifically, to a semiconductor wafer processing apparatus including a semiconductor wafer polishing pad and a semiconductor wafer polishing pad conditioner, and to a method of conditioning a semiconductor wafer polishing pad.
2. Discussion of Related Art
Semiconductor chips are manufactured by forming consecutive layers on a semiconductor wafer substrate. One or more of the layers are usually polished in a process which has become known in the art as "chemical-mechanical polishing" (CMP). CMP generally involves the steps of locating a wafer on a polishing pad with the layer which has to be polished on an interface between the wafer and the polishing pad. The wafer and the polishing pad are then moved over one another. A slurry is introduced on the polishing pad. The polishing pad has an abrasive surface so that movement of the wafer and the polishing pad over one another results in a gradual removal of the layer.
The material of the slurry and of the wafer eventually builds up on the polishing pad so that the polishing pad becomes "glazed" over with these materials. The glazed materials have to be removed from time to time so that the polishing pad is "conditioned" for further polishing.
FIG. 1 of the accompanying drawings is a plan view illustrating one conventional method of polishing a wafer and conditioning a polishing pad which polishes the wafer. A circular semiconductor wafer 20 is located on a circular semiconductor wafer polishing pad 22. The polishing pad 22 is rotated in a direction 24 to polish the wafer 20. A semiconductor wafer polishing pad conditioning arm 26 is mounted at a pivot point 28 so as to sweep back and forth over the polishing pad 22. One or more pointed members, such as diamond points, are located on a head 30 of the arm 26. Back and forth pivoting of the arm causes the pointed member to scrape back and forth over a surface of the polishing pad 22. The polishing pad 22 is rotated while the pointed member scrapes over the surface thereof so that the member conditions the polishing pad 22 in a zig zag manner. The wafer 20 has a diameter which is less than half the diameter of the polishing pad 22, thus leaving enough space for the polishing pad 22 to be conditioned while the wafer 20 is being polished.
FIG. 2 is a plan view illustrating another conventional method of polishing a wafer. A wafer 32 is located on a polishing pad 34 and the polishing pad 34 is rotated in a direction 36 so that the polishing pad 34 moves over the wafer 32. The method illustrated in FIG. 2 has distinct advantages over the method illustrated in FIG. 1 since the polishing pad 34 moves over the wafer 32 with a small orbital radius which results in more uniform motion between different points of the wafer 32. Mechanisms may be employed to control rotation of the wafer 32 relatively to the polishing pad 34. The wafer 32 has a diameter which is more than half the diameter of the polishing pad 34. A central region of the polishing pad 34 therefore remains covered by the wafer 32 at all times. In order to condition the polishing pad 34, the wafer 32 has to be removed. The conditioning of the wafer 34 is therefore a step in series with polishing of the wafer 34. In order to increase throughput, apparatus and a method for conditioning a polishing pad is required wherein conditioning of the polishing pad 34 is done efficiently.